This invention relates generally to electrically heated glazing closures and, more particularly, to an electrically heated window provided with a second electrical circuit for effecting sharp angular bends in the window.
A well known expedient for defogging or deicing the windows of automotive vehicles and the like is the use of heating circuits comprised of electrical resistance elements. Sometimes these resistance elements are formed of an electrically conducting material superimposed or fused on the inboard or inner surface of the glass sheet in a pattern of parallel lines extending lengthwise of the sheet or in a generally horizontal direction when installed in the vehicle. These parallel lines are connected at their opposite ends to electrodes or bus bars located adjacent the opposite ends of the glass sheet and extending generally transversely thereof. The heating circuit is imprinted on the glass sheet prior to bending the same into the desired configuration.
In recent years, it has sometimes become desirable to provide one or more relatively sharp angled bends in the glazing closure to carry out styling features found in the adjacent sheet metal panels of the vehicle. One of the most successful techniques for producing sharply bent glass sheets is provided by the glass bending methods disclosed and claimed in U.S. Pat. Nos. 3,762,903 and 3,762,904, assigned to the assignee of the present invention, whereby an electrically conducting path is formed on at least one surface of the glass sheet along one or more lines about which it is desired to sharply bend the sheet. The sheet is then supported on a suitable gravity-type mold structure and heated in a furnace to a temperature corresponding to the softening point of the glass, causing it to sag by gravity into conformance with the shaping surfaces of the mold while simultaneously passing an electric current through said path or paths to heat the area of the glass sheet immediately adjacent said paths to a temperature above the aforementioned softening point, causing said sheet to bend sharply along said paths to form the relatively sharp angles therein. A problem is encountered in employing this technique to form sharp bends in glazing closures having heated circuits imprinted thereon because the electrically conducting paths of the bending circuit necessary for producing the sharp bends intersect the electrically conducting lines of the heating circuit which tend to dissipate some of the current otherwise intended solely for the bending circuit. The known "cross over" technique, which involves interposing or sandwiching an insulator between intersecting wires for electrically separating the same would involve at least one, and more likely two, additional printing steps in the printed dual-circuit arrangement herein contemplated, adding materially to the costs of production.